Method for forming a conductive ceramic glaze

ABSTRACT

A method for forming an electrically conductive glaze upon the outer surface of a ceramic mold form including the mixing of approximately 25 percent potash feldspar, approximately 22 percent flint, approximately 7 to 8 percent calcium carbonate, approximately 1 to 2 percent ball clay, approximately 2 to 4 percent kaolin, approximately 5 percent barium carbonate and approximately 35 percent red iron oxide, all percentages being taken by weight, the method including the addition of an amount of flocculent such as 20 percent magnesium sulfate solution to control the viscosity of the solution and thereby control the thickness of the layer formed upon the external surface of the ceramic mold form, also including preferably the spraying or dipping of the mold form in the resulting solution for coating thereof as well as the firing of the coated ceramic mold form in a furnace of approximately 2200 to 2300 degrees Fahrenheit for approximately a 30 hour cycle.

This is a division of U.S. Ser. No. 911,007 filed May 30, 1978,presently pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In the handling of chemicals and other dangerous substances, it isdesirable to use special rubber gloves which are manufactured withoutimperfections. The present invention provides a means for forming anelectrically conductive surface on a mold which is usable to form suchgloves thereon.

It is usual that ceramic molds are used as the form about which therubber is placed for making these high quality gloves. The presentmethod is usable for a glaze about the external surface of such aceramic mold which glaze itself is electrically conductive to facilitatethe monitoring for imperfections of the gloves formed thereon. Also theconductive surface serves to increase the flow of heat to the glove tofacilitate curing thereof.

In practice a glove will be formed about a ceramic mold having theconductive glaze formed by the present invention therearound. And thenprior to removal of the glove from the form, the form and the glove as aunit may be dipped in an electrolytic solution such that the conductiveglaze itself will act as one electrode and another electrode may beplaced in the electrolyte. In another method the glove need not bedipped in an electrolytic solution, but an electrode may be manually orotherwise caused to pass over the surface of the glove and visual arcingor a surge reading on a voltage or current meter will indicate animperfection. In either system application of a voltage differenceacross the two electrodes will cause electrical current to flow betweenthe electrodes only if an imperfection exists in the wall of the glovesat any point such that electric current may flow therethrough. Howeverif the glove is indeed a perfect glove having no apertures therethroughor pinholes the flow of current between the electrodes will beprevented. In this manner a glove can be tested for imperfections in aone-step process without requiring the removal of the glove from themold form and the placing of the glove in a special test apparatus.

2. Description Of The Prior Art

The main problem existing in the prior art in the forming ofelectrically conductive glazes for ceramic mold forms has been the lackof consistency of resistivity between one fired glaze and the next firedglaze. It is desirable to use a ceramic glaze having repeatablyconsistent surface resistivity. The prior art conductive glazes did nothave this quality but the method of forming a glaze as disclosed andclaimed in the present invention provides a simple means for forming theglaze and, most importantly, provides a repetitive consistency of thesurface resistivity of the glaze in the range of 50,000 ohms to 150,000ohms when the measurement is made at points 1 and 2 inches apart.

Also the components of the glaze of the present invention are reasonablyinexpensive as well as easily accessible and in this manner providesfurther advantages over conductive glazes of the prior art.

Most prior art conductive surfaces on molds are achieved by usingelectrically conductive coatings rather than using the ceramic itself asthe conducting agent. Conductive coatings tend to wear off quickly whennot using the present invention but a conductive ceramic glaze has avery extended useful lifetime.

SUMMARY OF THE INVENTION

The present invention provides a method for forming an electricallyconductive glaze on the external surface of a ceramic mold form. Themain components used in the glazing method include approximately byweight 25 percent feldspar, 22 percent flint, 7 percent calciumcarbonate, 2 percent ball clay, 3 percent kaolin, 5 percent bariumcarbonate and 35 percent red iron oxide.

This overall glazing composition is added to water in an approximateratio of 5 parts of the original composition to 3 to 5 parts water, oran amount of water is added to cause the resulting solution to assume aspecific gravity of 1.52, preferably, or at least within the range of1.48 to 1.55.

Preferably, the feldspar is a potash feldspar and the flint has beenfiltered through a #200 mesh filter. This entire composition is thenscreened by an electric shaker through a #150 mesh followed by theaddition of an amount of flocculent such as magnesium sulfate 20 percentsolution for adjusting of the viscosity of the final dipping solution.The magnesium sulfate solution is operable to allow the smoothapplication of the glazing formula to the external surface of the moldform. If necessary a deflocculent can also be utilized to controlviscosity.

This coated mold form is now placed in a furnace for firing at a maximumtemperature of approximately 2200 to 2300 degrees for a 30 hour cycle toform a black semi-gloss electrically conductive glaze on the externalsurface of the mold. This method is reproducible to provide a surfaceresistivity of 50,000 to 150,000 ohms when measured at points 1 and 2inches apart.

It is the preferred embodiment of the present invention to provide aceramic mold form having an electrically conductive glaze about theexternal surface thereof.

It is an object of the present invention to provide an electricallyconductive glaze upon the surface of a ceramic mold which isreproducible such that the glaze has a surface resistivity of 50,000 to150,000 ohms when measured at points 1 and 2 inches apart.

It is an object of the present invention to provide an electricallyconductive glazing method resulting in a black semi-gloss finish afterfiring.

It is an object of the present invention to provide a method for formingan electrically conductive glaze upon the external surface of a ceramicmold form which includes an adjustable viscosity, controllable by theaddition of an amount of flocculent or deflocculent to assure smoothflow during application of the glazing material upon the mold form priorto firing.

It is an object of the present invention to provide a method for forminga solution to place an electrically conductive glaze upon a ceramic moldwherein the thickness of the formed glaze is controlled by the adjustingof the specific gravity of the glazing solution.

It is an object of the present invention to provide an electricallyconductive composition for glazing a ceramic mold form wherein thespecific gravity is adjusted by controlling closely the amount of wateradded thereto prior to coating of the mold form.

It is an object of the present invention to provide a method for glazinga ceramic mold form including the firing of the coated mold form in aconveniently reproduceable manner to provide a constantly reproduceablesurface resistance of the resulting conductive glaze.

It is an object of the present invention to provide a method for formingan electrically conductive glaze on the external surface of a ceramicmold form which is usable with a variety of sizes of mold forms.

It is an object of the present invention to provide an electricallyconductive glaze upon a ceramic mold form which is capable of beingproduced for reasonably low cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the invention is particularly pointed out and distinctly claimedin the concluding portions herein, a preferred embodiment is set forthin this detailed description.

The purpose of the method of the present invention is to provide anelectrically conductive glaze upon the external surface of a ceramicmold form having a surface resistivity of approximately 50,000 to150,000 ohms when measured at points 1 and 2 inches apart but which iseasily reproducible within these tolerances. The preferred embodimentset forth in this detailed description provides a total material havinga weight of 20 pounds and 1 ounce. This material including potashfeldspar, flint, calcium carbonate, ball clay, kaolin, barium carbonateand red iron oxide is added to approximately 2 gallons of warm-to-hotwater such that the specific gravity of the resulting solution isapproximately 1.52. This solution is then adjusted for viscosity by theaddition of an amount of flocculent such as magnesium sulphate 20percent solution. Alternatively, if needed the addition of adeflocculent such as sodium tetrapyrophosphate or sodium silicate couldbe added. Then the ceramic mold form itself is coated and fired in orderto form the final electrically conductive glaze thereon.

Initially each of the ingredients listed below is weighed. The specificsof each of the seven components of the original material are listed inthe below table:

    __________________________________________________________________________                              PERCENTAGE TOLERANCES                               MATERIAL  LBS.                                                                             OZS.                                                                              PERCENTAGE                                                                             BY WEIGHT                                           __________________________________________________________________________    Feldspar (Potash)                                                                       5  4   26.2     24.0 to 28.0                                        Flint (200 Mesh)                                                                        4  7   22.2     20.0 to 24.0                                        Calcium Carbonate                                                                       9.7                                                                              15  9.7       5.0 to 10.0                                        Ball Clay 0  4   1.2       1.0 to 2.0                                         Kaolin    0  7   2.3       2.0 to 4.0                                         Barium Carbonate                                                                        0  14  4.4       4.0 to 6.0                                         Red Iron Oxide                                                                          6  14  34.0     30.0 to 36.0                                                  20 1   100.0                                                        __________________________________________________________________________

Initially in this preferred embodiment each of the seven materialslisted above is independently weighed. The iron oxide is hold separatelyand the remaining six ingredients are physically mixed. Initially theiron oxide is added to at least a portion of the 2 gallons of water andmixed. The mixing may be performed by stirring on an electric mixer forapproximately 10 minutes or possible ball milling for up to 3 hours. Theremaining six ingredients are then added and the entire composition isstirred for one-half hour. Additional water is now added to bring thespecific gravity within the limitations of 1.48 to 1.55 but mostpreferably to exactly 1.52. The exact amount of water finally added canvary within the tolerances and in this manner the final thickness of thecoating of material upon the external surface of the ceramic mold iscontrolled. Generally water will be added in an amount equal to 3 to 5parts water by weight to 5 parts of the original mixture. With a higherspecific gravity the coating will be thicker whereas with a lowerspecific gravity the coating will be thinner. This adjustment can bemade with each run in order to vary the thickness of the finalconductive glaze.

This solution now having the desired specific gravity may be screened toa #150 mesh on a shaker such as an electric shaker or the like. Then theviscosity of the solution is adjusted to assure a smooth applicationflow during the dipping or spraying steps by the addition of an amountof magnesium sulphate 20 percent solution which acts as a flocculent.This solution is added quite sparingly since a few drops will change theviscosity substantially due to chemical reaction with the material.However should deflocculent be needed then a small amount of sodiumtetrapyrophospate or sodium silicate may be added.

The now properly dipped or sprayed, wet ceramic mold form will be placedwithin a furnace for firing. Preferably the firing will be performed inan oxidizing environment wherein the temperature is raised toapproximately 2260 degrees Fahrenheit and then down to room temperatureover a 30 hour cycle. This will result in a black semi-gloss finishbeing assumed by the electrically conductive glaze as well as a surfaceresistivity in the range of 50,000 to 150,000 ohms when measured atpoints 1 and 2 inches apart.

One of the primary advantages of the method of the present invention isthe ability to consistently produce electrically conductive glazeshaving surface resistivity within the above-defined tolerances. As longas each of the materials is included within the percentage rangesclaimed and disclosed in this invention this surface resistivity will bemaintained within the described limit. Thus a consistency of resistivityin the resulting glaze is achieved by using the composition disclosedand claimed in the present invention as well as the method disclosed andclaimed herein.

While particular embodiments of this invention have been describedabove, it will be apparent, that many changes may be made in the form,arrangement and positioning of the various elements of the combination.In consideration thereof it should be understood that preferredembodiments of this invention disclosed herein are intended to beillustrative only and not intended to limit the scope of the invention.

I claim:
 1. A method for forming an electrically conductive glaze upon aceramic mold form comprising:(a) forming a combination comprisingfeldspar (24.0-28.0 percent by weight), flint (20.0-24.0 percent byweight), calcium carbonate (5.0-10.0 percent by weight), ball clay(1.0-2.0 percent by weight), kaolin (2.0-4.0 percent by weight), bariumcarbonate (4.0-6.0 percent by weight), red iron oxide (30.0-36.0 percentby weight); (b) forming a solution by mixing five parts by weight ofsaid combination with from three to five parts water by weight; (c)adjusting the viscosity of the solution as desired by adding an amountof flocculent or deflocculent thereto; (d) applying the solution to thesurface of a ceramic mold form; and (e) heating the coated ceramic moldform to form an electrically conductive glaze thereon.
 2. The method asdefined in claim 1 wherein said mixing is performed with sufficientwater to yield a resulting solution having a specific gravity of from1.48 to 1.52.
 3. The method as defined in claim 1 wherein the heating isperformed by the temperature of approximately 2260° F. for a cycle ofapproximately 30 hours.
 4. The method as defined in claim 1 wherein theapplying of the solution is performed by dipping of the ceramic moldform therein.
 5. The method as defined in claim 1 wherein the applyingof the solution is performed by spraying of the ceramic mold formtherein.
 6. The method as defined in claim 1 further including screeningof the solution through a #150 mesh filter after adjusting the specificgravity and prior to the adjusting of the viscosity by adding of the 20percent magnesium sulfate solution.